In recent years, there has been a demand for larger and thinner displays along with the spread of digital broadcasting. In response to such demand, flat panel displays such as liquid crystal displays and plasma displays are being developed and are proliferating. In flat panel displays, since the number of pixels is fixed according to the panel, it is necessary to perform resolution conversion and generate interpolation pixels in a case where the input image and panel resolutions differ.
According to “Handbook of Image Analysis [Revised Edition]” (Supervising Editors, Mikio Takagi, Haruhisa Shimoda, Sep. 10, 2004, University of Tokyo Press), there are pixel interpolation methods such as a nearest neighbor interpolation method which uses a reference pixel nearest to an interpolation pixel as the interpolation pixel value, a bilinear interpolation method which calculates an interpolation pixel value with weighted added distance by using pixel values of four points surrounding an interpolation pixel, and a cubic convolution method which calculates an interpolation pixel value with weighted distance by using pixel values of four points surrounding an interpolation pixel.
In Japanese Laid-Open Patent Publication No. 2005-107437, an interpolation pixel value is calculated by extracting a sharp edge area by a neighboring pixel difference, performing bilinear pixel interpolation with respect to the sharp edge area, performing cubic convolution with respect to other areas, and adding the weighted interpolation pixel value obtained by the bilinear pixel interpolation and the weighted interpolation pixel value obtained by the cubic convolution with respect to a boundary area. In Japanese Laid-Open Patent Publication No. 2004-96715, pixel interpolation is performed by selecting a pixel interpolation method such as the nearest neighbor interpolation method or the cubic convolution method according to number of colors of an image, edge strength of an image, or sharpness of an image. In Japanese Laid-Open Patent Publication No. 2002-101296, pixel interpolation is performed by using a bilinear interpolation function as one interpolation function and using a cubic convolution function as the other interpolation function. In Japanese Laid-Open Patent Publication No. 2000-151990, pixel interpolation is performed by using bilinear interpolation in a case where color is skin color or sky-blue color and using cubic convolution in other cases.